Local epidemic history as a predictor of tuberculosis incidence in Saskatchewan Aboriginal communities.

BACKGROUND

Average tuberculosis (TB) incidence rates are high in Canadian Aboriginal communities, but there is significant variability within this group.

OBJECTIVE

To determine whether local history of post-contact TB epidemics is predictive of contemporary epidemiology among Aboriginal communities in Saskatchewan, Canada.

METHODS

TB incidence, age-specific morbidity patterns and rates of clustering of TB genotypes from 1986 to 2004 were compared between two groups of communities: Group 1, in which post-contact epidemics of TB were established around 1870, and Group 2, in which they were delayed until after 1920. Concomitant effects of socio-economic and geographic variables were explored with multivariate models.

RESULTS

Group 2 communities were characterized by higher annual incidence of TB (median 431 per 100,000 population vs. 38/100,000). In multivariate models that included socio-economic and geographic variables, historical grouping remained a significant independent predictor of community incidence of TB. Clustering of TB genotypes was associated with Group 2 (OR 8.7, 95%CI 3.3-22.7) and age 10-34 years (OR 2.5, 95%CI 1.1-5.7).

CONCLUSIONS

TB transmission dynamics can vary significantly as a function of a population's historical experience with TB. Populations at different stages along the epidemic trajectory may be amenable to different types of interventions.